1. Field of the Invention
The present invention relates to a coating device. More specifically, the present invention is directed to a coating device for cast coating webs, plates or the like, comprising a coating material supply tank and a pump for pumping coating material from the supply tank through a hose into a supply pipe which opens into a casting channel.
2. Description of the Prior Art
Cast coating is typically carried out in the form of a curtain coating, whereby coating material is conveyed downward through a slot die of a coating head, and upon emerging from a narrow die gap, the coating material is pulled down by gravity and forms a curtain.
In another known coating device, commonly known as a "sliding surface coater", the coating material is conveyed upward through a duct and flows down an inclined surface. At a breaking edge of this inclined surface, the coating material forms a curtain which coats a substrate as it is transported past the coater.
In other known coating devices, coating material flows through a vat out of which it is scooped by means of a rotating roll. A metering blade provided adjacent the rotating roll shaves the coating material off the rotating roll, and the shaved coating material flows down an inclined surface to an edge of the inclined surface, where the coating material is pulled down by gravity and forms a cast curtain.
All of these coating devices use narrow gaps to produce the coating film, the cleanliness and precision of which have a considerable influence on the resulting coating. After the casting operation, the casting heads of these coating devices must, in general, be cleaned very thoroughly to prevent coating residues from drying up and hardening which could give rise to faults in the curtain when the coating devices are started again. For this purpose, the slot dies of the casting heads must be opened or cleaned from the inside using large quantities of solvents and diluents. This procedure requires considerable expenditure in terms of manpower and time and consumes large amounts of solvents and detergents, which must be recovered in an ecologically acceptable process and stored. In practice, cleaning of the coating devices is often avoided by keeping the coating line in operation round-the-clock, even when it is not used for production, for example overnight. In such a case, however, the solvent evaporating from the coating material must be continuously replenished, which means that this way of proceeding is cost-intensive and hardly economical.
To keep down-times due to cleaning operations on the coating devices as short as possible, the component parts of coating devices, which must be cleaned, are often exchangeable. For cleaning purposes, the casting heads and coating material containers can then be exchanged, for example, if a different coating material is to be used. The cleaning of casting heads and other component parts of the coating devices is then carried out remote from the coating line.
Curtain coating is used, among others, to apply photosensitive solder stop resists to circuit boards or to apply liquid galvano or etch resists to support materials. The photosensitive solder stop resists are usually two-component systems comprising a resist material and a hardening agent that hardens after a certain period of time. This means that regular and proper cleaning of the coating device is particularly important in order to keep the coating device always ready for operation.